Waveguides are used to guide electromagnetic, light, or sound waves. The type of waveguide is dependent on the type of wave to be propagated. The most common waveguide design is a simple hollow metal conductor tube inside which the wave travels, eventually exiting and propagating outward and away from the exit point of the tube. For certain types of waveguide's wherein the wave is kept in a confined medium (air filled waveguide, dielectric filled waveguide, slot-line waveguide, slot-based waveguide etc.) waveguide interface is the only physical means to connect different waveguide components together to allow the waves to propagate therethrough.
Typical waveguides are made from materials such as brass, copper, silver, aluminum, or any other metal that has low bulk resistivity. Waveguide structures have conventionally been assembled in several ways. Dip-brazing is a process for joining aluminum waveguides, wherein a thin doping layer is applied at the point of connection, thereby lowering the melting point at that one contact point so the waveguides may be joined. Electroforming allows the entire waveguide structure to be built up layer by layer through electroplating. Other methods include electronic discharge machining and computerized numerically controlled machining.
Waveguides are becoming more commonly used in the millimeter wave and sub-millimeter wave industry, which includes frequencies above 30 GHz. This high band of electromagnetic waves is currently beginning to be used on many new devices and services, such as high-resolution radar systems, point-to-point communications and point-to-multipoint communications.
Because in general, higher frequency waves require a smaller waveguide, it is very important in the millimeter wave and sub-millimeter wave range that waveguides be machined very precisely. At the smallest sizes even the highest machining tolerances begin to present problems. For instance, to propagate frequencies above 110 GHz, the precision with which the waveguide flanges must be machined is greater than can easily be achieved. Hence, at frequencies of 110 GHz and above, it is common for the waveguide interface to become the weak link in a system.
Under the current standardizations objectives by the U.S. Department of Defense (hereinafter “MIL Spec”) for specified tolerances and the standard alignment pins to alignment holes method, the smaller the waveguide, the greater the relative misalignment and the greater the impact to the system electrical performance. The problem becomes so great that at 680 GHz, the flange and the waveguide can be misaligned as much as a quarter of a wavelength—that is, half the physical waveguide dimension. The problem is detectable at frequencies as low as 200 GHz, and begins impacting electrical performance severely as frequency approaches 400 GHz.
The effect of waveguide misalignment is degraded electrical performance of the waveguide, such as increased voltage standing wave ratio (VSWR). The more accurately the waveguide interfaces are aligned, the better behaved and more predictable is the waveguide system performance.
There is thus a need for an improved waveguide interface design that offers improved performance repeatability, VSWR frequency response and a more robust mechanical handling without the use of conventional alignment pins to alignment holes techniques.